Generation of Intermittent Jet by Pulse-Modulated Synthetic Jets
Broučková, Zuzana
2018 - English
An axisymmetric air jet was excited using a pair of counter synthetic jets running in opposed direction. First, the control synthetic jets were measured alone. The driving signal was pulse modulated sinusoidal signal. After an adjustment, the primary axisymmetric jet was excited to the bifurcating mode, and its behavior was studied experimentally. For comparison purposes, a reference steady (unforced) jet from the same nozzle was also measured (Reynolds number was approximately 1300). The flow visualization and hot-wire anemometry techniques were used.
Keywords:
synthetic jet; pulse modulation; flow controlAvailable at various institutes of the ASCRGeneration of Intermittent Jet by Pulse-Modulated Synthetic Jets

An axisymmetric air jet was excited using a pair of counter synthetic jets running in opposed direction. First, the control synthetic jets were measured alone. The driving signal was pulse modulated ...

Broučková, Zuzana
Ústav termomechaniky, 2018

The Influence of Different Geometries of Human Vocal Tract Model on Resonant Frequencies
Valášek, Jan; Sváček, Petr; Horáček, Jaromír
2018 - English
This paper presents the transfer function approach in order to determine the acoustic resonant frequencies of a human vocal tract model. The transfer function is introduced here as an acoustic pressure ratio between input amplitude at glottis position and output amplitude at mouth opening given by the solution of Helmholtz equation. This equation is numerically approximated by finite element method. The influence of different boundary conditions are studied and also different locations of excitation and microphone. \nFour different vocal tract geometries motivated by vocal tract geometry for vowel [u:] are investigated. Its acoustic resonance frequencies in range 100 - 2500 Hz are computed and compared with published results.\nFurther, the transient acoustic computation with different acoustic analogies are performed. The frequency spectra of Lighthill analogy, acoustic wave equation and perturbed convective wave equation are compared, where the vocal tract model with best frequency agreement with published results was chosen. The dominant frequencies correspond with predicted frequencies of transfer function approach.\n
Keywords:
wave equation; transfer function; aeroacoustic analogies; perfectly matched layerAvailable at various institutes of the ASCRThe Influence of Different Geometries of Human Vocal Tract Model on Resonant Frequencies

This paper presents the transfer function approach in order to determine the acoustic resonant frequencies of a human vocal tract model. The transfer function is introduced here as an acoustic ...

Numerical investigation of acoustic characteristics of 3D human vocal tract model with nasal cavities
Vampola, T.; Štorkán, J.; Horáček, Jaromír; Radolf, Vojtěch
2018 - English
Acoustic resonance characteristics of 3D human vocal tract model without and with nasal and\nparanasal cavities were computed. Nasal cavities (NC) form the side branches of the human vocal tract and exhibit antiresonance and resonance properties which influence the produced voice quality. Developed FE models of acoustic spaces of nasal and vocal tract for vowel /a:/ are used to study the influence of (NC) on phonation. Acoustics frequency-modal characteristics are studied by modal analysis and numerical simulation of acoustic signals in time domain is performed by transient analysis of the FE models.
Keywords:
formant frequencies; modelling of phonation; biomechanics of voiceAvailable at various institutes of the ASCRNumerical investigation of acoustic characteristics of 3D human vocal tract model with nasal cavities

Acoustic resonance characteristics of 3D human vocal tract model without and with nasal and\nparanasal cavities were computed. Nasal cavities (NC) form the side branches of the human vocal tract and ...

Acoustic characteristics of 3D human vocal tract model with nasal cavities – preliminary experimental results
Radolf, Vojtěch; Horáček, Jaromír; Košina, Jan; Vampola, T.
2018 - English
Acoustic resonance characteristics of 3D human vocal tract model with nasal and paranasal cavities were measured in three different ways: The excitation was realized by (1) self-oscillating vocal folds replica, (2) by a swept harmonic signal from an earphone placed instead of the vocal folds and (3) by a white noise signal from a loudspeaker located in front of the open mouth of the model. Resulting resonance frequencies are comparable for all excitation signals. These experiments were carried out to verify a complex mathematical model.
Keywords:
formant frequencies; transfer function; biomechanics of voiceAvailable at various institutes of the ASCRAcoustic characteristics of 3D human vocal tract model with nasal cavities – preliminary experimental results

Acoustic resonance characteristics of 3D human vocal tract model with nasal and paranasal cavities were measured in three different ways: The excitation was realized by (1) self-oscillating vocal ...

Self-excited oscillation properties of the profile NACA0015 in subsonic flow
Zolotarev, Igor; Vlček, Václav; Kozánek, Jan
2018 - English
Self-excited oscillations of the profile NACA0015 in subsonic flow were realized in the wind tunnel. The plunge support had the same elasticity for all experiments, the pitch support had seven different elasticity parameters. During our experiments different types of selfexcited vibration (flutter, stall flutter) were observed. Range of Mach numbers was M = 0.08–0.45, corresponding range of Reynolds numbers is Re = (1–5)·105, when the chord length is used as the characteristic dimension of the profile.\n
Keywords:
airfoil; aeroelasticity; stall flutter; dynamic stall; limit cycle oscillation; self-excited vibrationAvailable at various institutes of the ASCRSelf-excited oscillation properties of the profile NACA0015 in subsonic flow

Self-excited oscillations of the profile NACA0015 in subsonic flow were realized in the wind tunnel. The plunge support had the same elasticity for all experiments, the pitch support had seven ...

Vibration stability of a vertical flywheel lifted by permanent magnetic rings
Zapoměl, Jaroslav; Ferfecki, P.; Sudhakar, A.; Kozánek, Jan
2018 - English
Lifting the vertical flywheels by permanent magnets is used to reduce energy losses in the support elements. Unstable equilibrium position of pairs of magnetic rings, material damping of the shaft, and nonlinear properties of the support elements can arrive at the flywheel unstable oscillations. Therefore, evaluation of the vibration stability is the essential part of the design process of flywheel devices. In the developed computational procedure the flywheel is represented by a beam-like body, to which an absolutely rigid disc (the actual flywheel) is attached. The determination of the force action between the magnetic rings is based on mutual interaction between two magnetic dipoles. The steady state response of the flywheel on the unbalance excitation is calculated by means of the trigonometric collocation method and its stability is evaluated by application of the Floquet theorem. The developed computational procedures and learning more on behaviour of flywheels lifted by magnetic rings are the main contributions of the carried out research.\n
Keywords:
vertical flywheels; permanent magnets; vibration stabilityAvailable at various institutes of the ASCRVibration stability of a vertical flywheel lifted by permanent magnetic rings

Lifting the vertical flywheels by permanent magnets is used to reduce energy losses in the support elements. Unstable equilibrium position of pairs of magnetic rings, material damping of the shaft, ...

Synthetic Jet Characteristic Velocity Estimated nn The Basis of Momentum Flux Measurement
Kordík, Jozef; Trávníček, Zdeněk
2018 - English
The paper compares two methods of evaluation of synthetic jet characteristic velocity. The first method of the characteristic velocity estimation is based on a simple measurement of the synthetic jet momentum flux (the jet thrust) by means of precision scales. The second method is a standard one, it is based on spatial-temporal integration of the velocity profile at the synthetic jet actuator nozzle exit. The velocity profile was obtained here using hotwire measurements in air. Comparison of the methods is based on dimensionless stroke length of the synthetic jet. It is confirmed that the results of both methods are nearly the same for higher dimensionless stroke length. On the other hand, if the jet regime approaches to the synthetic jet criterion threshold (i.e. to the dimensionless stroke length of 0.5) the results of both methods diverge. Using the current results a correction is suggested for the momentum-flux-based method to match the standard one.
Keywords:
synthetic jet; synthetic jet actuator; momentum fluxAvailable at various institutes of the ASCRSynthetic Jet Characteristic Velocity Estimated nn The Basis of Momentum Flux Measurement

The paper compares two methods of evaluation of synthetic jet characteristic velocity. The first method of the characteristic velocity estimation is based on a simple measurement of the synthetic jet ...

The texts of the abstracts were set individually by the authors. Any options, findings and conclusions or recommendations expressed in this book are those of the individual authors on their own ...

Nosek, Štěpán; Kočí, K.
Ústav termomechaniky, 2018

Experimental investigation of acoustic characteristics of 3D human vocal tract model with nasal cavities
Radolf, Vojtěch; Horáček, Jaromír; Košina, Jan; Vampola, T.
2018 - English
The following experiments were carried out to be later used in the verification of a complex\nmathematical model of human voice production. Acoustic resonance characteristics of a 3D human voca tract model without and with nasal and paranasal cavities were measured in two different ways: The excitation was realized by (1) self-oscillating vocal folds replica and (2) by sine-tone sweeps from an earphone placed instead of the vocal folds. The resulting resonance and antiresonance frequencies were found to be comparable for both excitation signals.
Keywords:
formant frequencies; modelling of phonation; biomechanics of voiceAvailable at various institutes of the ASCRExperimental investigation of acoustic characteristics of 3D human vocal tract model with nasal cavities

The following experiments were carried out to be later used in the verification of a complex\nmathematical model of human voice production. Acoustic resonance characteristics of a 3D human voca tract ...

Dynamics of four-planetary gearing box
Půst, Ladislav; Pešek, Luděk; Škuderová, Alena
2018 - English
Planetary gearboxes are more complicated than parallel-axis gear transmission systems and\ntherefore they need deeper dynamic analysis, which is important for reduction of noise and vibration. The main advantage of planetary gearings is the splitting of force flow into several planet wings, but it can be devaluated by unequal load sharing on planet stages. For improving, the floating sun wheal and flexible pins of planets are applied. Dynamic model of such a gearing box is derived in the paper and it is shown that the frequency spectrum contains many multiple eigen-frequencies. Examples of several eigen-modes and transfer functions of this four-planetary gearing box are presented as well. The problem of dimensional nonhomogeneous vectors and matrix is also mentioned.
Keywords:
planetary gearing; frequency spectrum; multiple eigenvalues; eigen-modesAvailable at various institutes of the ASCRDynamics of four-planetary gearing box

Planetary gearboxes are more complicated than parallel-axis gear transmission systems and\ntherefore they need deeper dynamic analysis, which is important for reduction of noise and vibration. The ...

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